The attenuated end of the phenotypic spectrum in MPS III: from late-onset stable cognitive impairment to a non-neuronopathic phenotype

Causes of death in mucopolysaccharidoses

Mucopolysaccharidoses are inherited metabolic diseases caused by mutations in genes encoding enzymes required for degradation of glycosaminoglycans. A lack or severe impairment of activity of these enzymes cause accumulation of GAGs which is the primary biochemical defect. Depending on the kind of the deficient enzyme, there are 12 types and subtypes of MPS distinguished. Despite the common primary metabolic deficit (inefficient GAG degradation), the course and symptoms of various MPS types can be different, though majority of the diseases from the group are characterized by severe symptoms and significantly shortened live span. Here, we analysed the frequency of specific, direct causes of death of patients with different MPS types, the subject which was not investigated comprehensively to date. We examined a total of 1317 cases of death among MPS patients, including 393 cases of MPS I, 418 cases of MPS II, 232 cases of MPS III, 45 cases of MPS IV, 208 cases of MPS VI, and 22 cases of MPS VII. Our analyses indicated that the most frequent causes of death differ significantly between MPS types, with cardiovascular and respiratory failures being predominant in MPS I, MPS II, and MPS VI, neurological deficits in MPS III, respiratory issues in MPS IV, and hydrops fetalis in MPS VII. Results of such studies suggest what specific clinical problems should be considered with the highest priority in specific MPS types, apart from attempts to correct the primary causes of the diseases, to improve the quality of life of patients and to prolong their lives.

Non-syndromic retinal dystrophy associated with biallelic variation of SUMF1 and reduced leukocyte sulfatase activity

Biallelic variants in SUMF1 are associated with multiple sulfatase deficiency (MSD), a rare lysosomal storage disorder typically diagnosed in early infancy or childhood, marked by severe neurodegeneration and early mortality. We present clinical and molecular characterisation of three unrelated patients aged 13 to 58 years with milder clinical manifestations due to SUMF1 disease variants, including two adult patients presenting with apparent non-syndromic retinal dystrophy. Whole genome sequencing identified biallelic SUMF1 variants in all three patients; Patient 1 homozygous for a complex allele c.[290G>T;293T>A]; p.[(Gly97Val);(Val98Glu)], Patient 2 homozygous for c.866A>G; p.(Tyr289Cys), and Patient 3 compound heterozygous for c.726-1G>C and p.(Tyr289Cys). Electroretinography indicated a rod-cone dystrophy with additional possible inner retinal dysfunction in all three patients. Biochemical studies confirmed reduced, but not absent, sulfatase enzyme activity in the absence of extra-ocular disease (Patient 1) or only mild systemic disease (Patients 2, 3). These cases are suggestive that non-null SUMF1 genotypes can cause an attenuated clinical phenotype, including retinal dystrophy without systemic complications, in adulthood.

Late-onset mucopolysaccharidosis type IIIA mimicking Usher syndrome

Mucopolysaccharidosis type IIIA (MPS IIIA or Sanfilippo syndrome type A) is an autosomal recessive lysosomal storage disorder caused by pathogenic variants in the SGSH gene encoding N-sulfoglucosamine sulfohydrolase, an enzyme involved in the degradation of heparan sulfate. MPS IIIA is typically characterized by neurocognitive decline and hepatosplenomegaly with childhood onset. Here, we report on a 53-year-old male subject initially diagnosed with Usher syndrome for the concurrence of retinitis pigmentosa and sensorineural hearing loss. Clinical exome sequencing identified biallelic missense variants in SGSH, and biochemical assays showed complete deficiency of sulfamidase activity and increased urinary glycosaminoglycan excretion. Reverse phenotyping revealed left ventricle pseudo-hypertrophy, hepatosplenomegaly, bilateral deep white matter hyperintensities upon brain MRI, and decreased cortical metabolic activity by PET-CT. On neuropsychological testing, the proband presented only partial and isolated verbal memory deficits. This case illustrates the power of unbiased, comprehensive genetic testing for the diagnosis of challenging mild or atypical forms of MPS IIIA.

Repetitive, non-invasive imaging of neurodegeneration, and prevention of it with gene replacement, in mice with Sanfilippo syndrome

Hampering assessment of treatment outcomes in gene therapy and other clinical trials in patients with childhood dementia is the lack of an objective, non-invasive measure of neurodegeneration. Optical coherence tomography (OCT) is a widely available, rapid, non-invasive, and quantitative method for examining the integrity of the neuroretina. Profound brain and retinal dysfunction occur in patients and animal models of childhood dementia, including Sanfilippo syndrome and we recently revealed a correlation between the age of onset and rate of progression of retinal and brain degeneration in sulfamidase-deficient Sanfilippo mice. The aim of the current study was to use OCT to visualise the discrete changes in retinal structure that occur during disease progression. A progressive decline in retinal thickness was readily observable in Sanfilippo mice using OCT, with differences seen in affected animals from 10-weeks of age. OCT applied to i.v. AAV9-sulfamidase-treated Sanfilippo mice enabled visualisation of improved retinal anatomy in living animals, an outcome confirmed via histology. Importantly, brain disease lesions were also ameliorated in treated Sanfilippo mice. The findings highlight the sensitivity, ease of repetitive use and quantitative capacity of OCT for detection of discrete changes in retinal structure and their prevention with a therapeutic. Combined with the knowledge that retinal and brain degeneration are correlated in Sanfilippo syndrome, OCT provides a window to the brain in this and potentially other childhood dementias.

Biochemical diagnosis of Sanfilippo disorder types A and B

BACKGROUND

One of the 11 recognized mucopolysaccharidosis (MPS) diseases is Sanfilippo. It is autosomal recessive in its mode of transmission. There are four subtypes of Sanfilippo (A, B, C, and D). The most worldwide prevalent subtypes of mucopolysaccharidosis type III (MPS III) are A and B followed by C and D subtypes. To estimate the frequency of MPS IIIA among MPS III patients, we diagnose and compare their clinical features with those of MPS IIIB and also compare the prevalence of MPS IIIB versus MPS IIIA among diagnosed cases at the Biochemical Genetic Department at NRC. For every case that was referred, the quantitative determination of urine Glycosaminoglycans (GAGs) was assessed. Two-dimensional electrophoresis (2DE) of GAGs extracted from urine was performed on all cases with high urinary GAG levels. Both N-sulphoglucosamine sulphohydrolase (MPS IIIA) and N-alpha-acetylglucosaminidase (MPS IIIB) enzyme activity were determined fluorometrically.

RESULTS

From November 2019 to May 2022, 535 cases were referred to the National Research Centre's Biochemical Genetics Department. 233 (43%) MPS cases were diagnosed with high urinary GAG levels for their ages. 73 (31.3%) MPS III cases were diagnosed by 2DE out of the 233 MPS cases. Plasma N-alpha-acetylglucosaminidase enzyme assay was insufficient in 36 (49.3%) patients (Sanfilippo type B), while N-sulphoglucosamine sulphohydrolase enzyme activity was deficient in 15 (20.6%) patients. The other 22 (30.1%) patients are either Sanfilippo type C or D.

CONCLUSION

N-sulphoglucosamine sulphohydrolase enzyme activity was measured for the first time in Egypt. Thirty-one percent of all diagnosed MPS cases during the last 3 years were MPS type III, making Sanfilippo the most common MPS type among the referred cases to our Biochemical Genetics Department. MPS IIIA accounts for 20.6% of MPSIII cases in this study. Still, MPS type IIIB is the commonest type among diagnosed patients.

Clinical, biochemical, and molecular characterization of mucopolysaccharidosis type III in 34 Egyptian patients

Mucopolysaccharidosis type III (MPS III) is a rare autosomal recessive lysosomal storage disorder characterized by progressive neurocognitive deterioration. There are four MPS III subtypes (A, B, C, and D) that are clinically indistinguishable with variable rates of progression. A retrospective analysis was carried out on 34 patients with MPS III types at Cairo University Children's Hospital. We described the clinical, biochemical, and molecular spectrum of MPS III patients. Of 34 patients, 22 patients had MPS IIIB, 7/34 had MPS IIIC, 4/34 had MPS IIIA, and only 1 had MPS IIID. All patients presented with developmental delay/intellectual disability, and speech delay. Ataxia was reported in a patient with MPS IIIC, and cerebellar atrophy in a patient with MPS IIIA. We reported 25 variants in the 4 MPS III genes, 11 of which were not previously reported. This is the first study to analyze the clinical and genetic spectrum of MPS III patients in Egypt. This study explores the genetic map of MPS III in the Egyptian population. It will pave the way for a national registry for rare diseases in Egypt, a country with a high rate of consanguineous marriage and consequently a high rate of autosomal recessive disorders.

Histological characterization of retinal degeneration in mucopolysaccharidosis type IIIC

Heparan-α-glucosaminide N-acetyltransferase (HGSNAT) participates in lysosomal degradation of heparan sulfate. Mutations in the gene encoding this enzyme cause mucopolysaccharidosis IIIC (MPS IIIC) or Sanfilippo syndrome type C. MPS IIIC patients exhibit progressive neurodegeneration, leading to dementia and death in early adulthood. Currently there is no approved treatment for MPS IIIC. Incidences of non-syndromic retinitis pigmentosa and early signs of night blindness are reported in some MPS IIIC patients, however the majority of ocular phenotypes are not well characterized. The goal of this study was to investigate retinal degeneration phenotype in the Hgsnat knockout mouse model of MPS IIIC and a cadaveric human MPS IIIC eye. Cone and rod photoreceptors in the eyes of homozygous 6-month-old Hgsnat knockout mice and their wild-type counterparts were analyzed using cone arrestin, S-opsin, M-opsin and rhodopsin antibodies. Histological observation was performed on the eye from a 35-year-old MPS IIIC donor. We observed a nearly 50% reduction in the rod photoreceptors density in the Hgsnat knockout mice compared to the littermate wild-type controls. Cone photoreceptor density was unaltered at this age. Severe retinal degeneration was also observed in the MPS IIIC donor eye. To our knowledge, this is the first report characterizing ocular phenotypes arising from deleterious variants in the Hgsnat gene associated with MPS IIIC clinical phenotype. Our findings indicate retinal manifestations may be present even before behavioral manifestations. Thus, we speculate that ophthalmological evaluations could be used as diagnostic indicators of early disease, progression, and end-point evaluation for future MPS IIIC therapies.

Neuropsychology assessment and outcomes in adult mucopolysaccharidosis - A systematic review as the first step to service development in a large tertiary Lysosomal Storage Disorders centre

A systematic review of Randomised Controlled Trials in adult mucopolysaccharidoses (MPSs) was conducted to inform neuropsychology service development at a large tertiary Lysosomal Storage Diseases centre. Studies including psychological endpoints for cognition, mood, and quality of life were reviewed. Forty-eight studies met the inclusion criteria for full text review. Of the 48 studies, 44% (21/48) included adult participants, while psychological endpoints were used in 52% (25/48) for cognition, 11% (5/48) for mood, and 69% (33/48) for quality of life. Five studies included both adult participants and relevant psychological endpoints. Risk of bias ratings were 'high' for two studies, while two studies received a rating of 'some concerns', and the last study a 'low' risk of bias rating. The evidence base for psychological outcomes in adult MPS disorders is limited and insufficient for guiding neuropsychology service development. Data on the psychosocial effects of MPS across the lifespan will be crucial for planning service development and supporting the neuropsychological needs of adult patients and their families.

Neurological, neurobehavioral, and radiological alterations in patients with mucopolysaccharidosis III (Sanfilippo's syndrome) in Brazil

Mucopolysaccharidosis type III (MPS III) or Sanfilippo syndrome is the most common form of MPS, in which neurological involvement in all stages of the disease is prominent. The current study aimed to comprehensively describe the neurological profile of children and adolescents with MPS III who visited the largest pediatric hospital in South America. A prospective/retrospective cohort analysis was performed on 10 patients with MPS III from eight unrelated families. Most patients <12 months of age had achieved development milestones within the expected range for their age, with delay in walking independently and first single word acquisition. Behavioral symptoms were reported in seven patients. Eight patients (80%) developed profound intellectual disabilities. Six patients (60%) had epilepsy, among whom 75% had their first seizure between 2 and 4 years of age; the frequency of which increased with age. Monotherapy was effective in 60% of patients. Two patients, both aged <8 years, had normal baseline electroencephalographic activity. Epileptiform activity was observed in three patients. Cortical atrophy was visualized using magnetic resonance imaging in 71% patients; all but one of these patients were aged >6 years. Neurological abnormalities increased in prevalence and severity with age. Anti-seizure drug resistance was uncommon. Dysmorphological and systemic manifestations were uncommon and mild and did not correlate with neurological involvement. Despite high allelic heterogeneity, neurodegeneration was similar among all patients. Overall, these data contribute to the scarce literature from developing countries.

Models to study basic and applied aspects of lysosomal storage disorders

The lack of available treatments and fatal outcome in most lysosomal storage disorders (LSDs) have spurred research on pathological mechanisms and novel therapies in recent years. In this effort, experimental methodology in cellular and animal models have been developed, with aims to address major challenges in many LSDs such as patient-to-patient variability and brain condition. These techniques and models have advanced knowledge not only of LSDs but also for other lysosomal disorders and have provided fundamental insights into the biological roles of lysosomes. They can also serve to assess the efficacy of classical therapies and modern drug delivery systems. Here, we summarize the techniques and models used in LSD research, which include both established and recently developed in vitro methods, with general utility or specifically addressing lysosomal features. We also review animal models of LSDs together with cutting-edge technology that may reduce the need for animals in the study of these devastating diseases.

Sanfilippo syndrome: consensus guidelines for clinical care

Sanfilippo syndrome is a group of rare, complex, and progressive neurodegenerative lysosomal storage disorders that is characterized by childhood dementia. The clinical management of patients with progressive neurological decline and multisystem involvement requires a multidisciplinary team with experience in the management of neurodegenerative disorders. Best practice guidelines for the clinical management of patients with these types of rare disorders are critical to ensure prompt diagnosis and initiation of appropriate care. However, there are no published standard global clinical care guidelines for patients with Sanfilippo syndrome. To address this, a literature review was conducted to evaluate the current evidence base and to identify evidence gaps. The findings were reviewed by an international steering committee composed of clinical experts with extensive experience in managing patients with Sanfilippo syndrome. The goal was to create a consensus set of basic clinical guidelines that will be accessible to and informed by clinicians globally, as well as providing a practical resource for families to share with their local care team who may not have experience with this rare disease. This review distills 178 guideline statements into an easily digestible document that provides evidence-based, expert-led recommendations for how to approach common management challenges and appropriate monitoring schedules in the care of patients with Sanfilippo syndrome.

Schizophreniform presentation and abrupt neurologic decline in a patient with late-onset mucopolysaccharidosis type IIIB

Due to their low frequency and some atypical presentations, inborn errors of metabolism are frequently misdiagnosed or underdiagnosed, which hinders the correct management of these patients. To illustrate that, here we present a patient that, at early school age, had learning disabilities compared to her classmates, especially for writing. She completed basic education in a regular school and was transferred to a secondary school for students with special needs. At 18 years of age, she presented a first psychiatric abrupt outbreak: she spent a month screaming and without sleeping. Behavioral problems then became apparent, especially hyperactivity, destructive and chaotic behavior, anxiety, and auto-aggressivity and hetero-aggressivity. A diagnosis of schizophreniform disorder was established. Clinical genetic evaluation revealed coarse face, macroglossia, coarse thick hair, and mild hepatomegaly, and the hypothesis of mucopolysaccharidosis-III was raised. Laboratory tests indicated high levels of urinary glycosaminoglycans and almost undetectable NAGLU activity, confirming the diagnosis. Sequencing of the NAGLU gene revealed the c.1318G>C (p.Gly440Arg) and c.1834A>G (p.Ser612Gly) mutations.

Mucopolysaccharidoses diagnosis in the era of enzyme replacement therapy in Egypt

BACKGROUND

Undegraded glycosaminoglycans (GAGs) induced by deficiency of enzymes are the primary cause of mucopolyscchardoses. Mucopolysacchardoses (MPS) are a group of rare lysosomal storage diseases (LSD). The quantification of a specific enzymatic activity is needed for accurate diagnosis. The objectives of this work were: first, to continue the study of mucopolysacchardoses disease in Egypt after the start of using the enzyme replacement therapy (ERT). Second, to define the commonest types among our population after 18 years experience with the disease. Third, to compare the different MPS types' distribution, diagnosed after the start of the ERT, to identify the impact of using ERT on the number and type of diagnosed patients.

METHOD

Urinary GAGs were measured for all referred cases followed by two-dimensional electrophoretic separation for cases with high levels of GAGs; the specific enzyme activity was assayed for each type depending on the abnormal electrophoretic pattern obtained. Clinically suspected cases of Morquio syndrome were directly subjected to measuring the specific enzyme.

RESULTS

Out of 1448 suspected cases, 622 (42.9%) MPS patients were diagnosed revealing the following distribution: MPS I (172, 27.7%), MPS II (57, 9.1%), MPS III [(177, 28.5%: 134 type B and 43 types A, C or D)], MPS IVA (124, 19.9%), MPS VI (90, 14.5%) and MPS VII (2, 0.3%). MPS III was the most commonly diagnosed type followed by MPS I and MPS IVA. MPS IVA represented the most common type receiving treatment, followed by MPS I, MPS II and MPS VI.

CONCLUSION

The presence of treatment encouraged the affected families and physicians to seek diagnosis. MPS III was the commonest type among our studied group after 7 years of diagnosis, while MPS IVA was the commonest type receiving treatment.

Electroclinical Features of Epilepsy in Mucopolysaccharidosis III: Outcome Description in a Cohort of 15 Italian Patients

Mucopolysaccharidosis III (Sanfilippo syndromes) types A-D are rare lysosomal storage disorders characterized by heparan sulfate accumulation and neurodegeneration. Patients with MPS III present with developmental stagnation and/or regression, sleep disturbance, and behavioral abnormalities usually in the first years of life. Epilepsy may occur in a proportion of patients during the disease course. However, the progression of epilepsy and EEG changes in MPS III have not been systematically investigated. We report electroclinical features in a cohort of patients with MPS III over a follow-up period ranging from 6.5 to 22 years. Participants include 15 patients (11 females; aged 7-31 years) with MPS III A (n = 7, 47%), MPS III B (n = 5, 34%), MPS III C (n = 2, 13%), and MPS III D (n = 1, 6%). At the time of this study, 8 out of 15 patients (53%) had epilepsy. Epilepsy occurred in patients with advanced disease even in the first decade of life (mean age at onset: 12.1 ± 6.7 years). However, seizure onset may also be associated with abrupt worsening of the neurobehavioral phenotype. The main epilepsy types observed were generalized (four out of eight, 50%), followed by focal (three out of eight, 37%) and combined (two out of eight, 25%) epilepsy and status epilepticus (one out of eight, 12.5%). Seizures were generally controlled by one antiepileptic drug (AED) and most patients (seven out of eight, 87%) were still on therapy after a median follow-up period of 5 years (range: 1-9 years). A total of 66 EEGs were analyzed with a median EEG follow-up duration of 7 years (range: 6 months-14 years). Slowing of the background activity occurred in 7 (46%) patients aged 4-19 years. Epileptiform EEG abnormalities were observed in 10 patients at a mean age of 9.6 ± 2.9 years. EEG epileptiform discharges were not unavoidably linked to epilepsy. Early recognition and careful monitoring of electroclinical features in MPS III is necessary for appropriate care and for the detection of disease progression.

Longitudinal MRI brain volume changes over one year in children with mucopolysaccharidosis types IIIA and IIIB

OBJECTIVE

To quantify changes in segmented brain volumes over 12 months in children with mucopolysaccharidosis types IIIA and IIIB (MPS IIIA and IIIB).

METHODS

In order to establish suitable outcome measures for clinical trials, twenty-five children greater than 2 years of age were enrolled in a prospective natural history study of MPS IIIA and IIIB at Nationwide Children's Hospital. Data from sedated non-contrast brain 3 T MRIs and neuropsychological measures were reviewed from the baseline visit and at 12-month follow-up. No intervention beyond standard clinical care was provided. Age- and sex-matched controls were gathered from the National Institute of Mental Health Data Archive. Automated brain volume segmentation with longitudinal processing was performed using FreeSurfer.

RESULTS

Of the 25 subjects enrolled with MPS III, 17 children (4 females, 13 males) completed at least one MRI with interpretable volumetric data. The ages ranged from 2.8 to 13.7 years old (average 7.2 years old) at enrollment, including 8 with MPS IIIA and 9 with MPS IIIB. At baseline, individuals with MPS III demonstrated reduced cerebral white matter and corpus callosum volumes, but greater volumes of the lateral ventricles, cerebellar cortex, and cerebellar white matter compared to controls. Among the 13 individuals with MPS III with two interpretable MRIs, there were annualized losses or plateaus in supratentorial brain tissue volumes (cerebral cortex -42.10 ± 18.52 cm³/year [mean ± SD], cerebral white matter -4.37 ± 11.82 cm³/year, subcortical gray matter -6.54 ± 3.63 cm³/year, corpus callosum -0.18 ± 0.62 cm³/yr) and in cerebellar cortex (-0.49 ± 12.57 cm³/year), with a compensatory increase in lateral ventricular volume (7.17 ± 6.79 cm³/year). Reductions in the cerebral cortex and subcortical gray matter were more striking in individuals younger than 8 years of age. Greater cerebral cortex volume was associated with higher fine and gross motor functioning on the Mullen Scales of Early Learning, while greater subcortical gray matter volume was associated with higher nonverbal functioning on the Leiter International Performance Scale. Larger cerebellar cortex was associated with higher receptive language performance on the Mullen, but greater cerebellar white matter correlated with worse adaptive functioning on the Vineland Adaptive Behavioral Scales and visual problem-solving on the Mullen.

CONCLUSIONS

Loss or plateauing of supratentorial brain tissue volumes may serve as longitudinal biomarkers of MPS III age-related disease progression compared to age-related growth in typically developing controls. Abnormally increased cerebellar white matter in MPS III, and its association with worse performance on neuropsychological measures, suggest the possibility of pathophysiological mechanisms distinct from neurodegeneration-associated atrophy that warrant further investigation.

The natural history of neurocognition in MPS disorders: A review

MPS disorders are associated with a wide spectrum of neurocognitive effects, from mild problems with attention and executive functions to progressive and degenerative neuronopathic disease. Studies of the natural history of neurocognition are necessary to determine the profile of abnormality and the rates of change, which are crucial to select endpoints for clinical trials of brain treatments and to make clinical recommendations for interventions to improve patients' quality of life. The goal of this paper is to review neurocognitive natural history studies to determine the current state of knowledge and assist in directing future research in all MPS disorders. There are seven different types of MPS diseases, each resulting from a specific enzyme deficiency and each having a separate natural history. MPS IX, will not be discussed as there are only 4 cases reported in the literature without cognitive abnormality. For MPS IH, hematopoietic cell transplant (HCT) is standard of care and many studies have documented the relationship between age at treatment and neurocognitive outcome, and to a lesser extent, neurocognitive status at baseline. However, the mortality and morbidity associated with the transplant process and residual long-term problems after transplant, have led to renewed efforts to find better treatments. Rather than natural history, new trials will likely need to use the developmental trajectories of the patients with HCT as a comparators. The literature has extensive data regarding developmental trajectories post-HCT. For attenuated MPS I, significant neurocognitive deficits have been documented, but more longitudinal data are needed in order to support a treatment directed at their attention and executive function abnormalities. The neuronopathic form of MPS II has been a challenge due to the variability of the trajectory of the disease with differences in timing of slowing of development and decline. Finding predictors of the course of the disease has only been partially successful, using mutation type and family history. Because of lack of systematic data and clinical trials that precede a thorough understanding of the disease, there is need for a major effort to gather natural history data on the entire spectrum of MPS II. Even in the attenuated disease, attention and executive function abnormalities need documentation. Lengthy detailed longitudinal studies are needed to encompass the wide variability in MPS II. In MPS IIIA, the existence of three good natural history studies allowed a quasi-meta-analysis. In patients with a rapid form of the disease, neurocognitive development slowed up until 42 to 47 months, halted up to about 54 months, then declined rapidly thereafter, with a leveling off at an extremely low age equivalent score below 22 months starting at about chronological age of 6. Those with slower or attenuated forms have been more variable and difficult to characterize. Because of the plethora of studies in IIIA, it has been recommended that data be combined from natural history studies to minimize the burden on parents and patients. Sufficient data exists to understand the natural history of cognition in MPS IIIA. MPS IIIB is quite similar to IIIA, but more attenuated patients in that phenotype have been reported. MPS IIIC and D, because they are so rare, have little documentation of natural history despite the prospects of treatments. MPS IV and VI are the least well documented of the MPS disorders with respect to their neurocognitive natural history. Because, like attenuated MPS I and II, they do not show progression of neurocognitive abnormality and most patients function in the range of normality, their behavioral, attentional, and executive function abnormalities have been ignored to the detriment of their quality of life. A peripheral treatment for MPS VII, extremely rare even among MPS types, has recently been approved with a post-approval monitoring system to provide neurocognitive natural history data in the future. More natural history studies in the MPS forms with milder cognitive deficits (MPS I, II, IV, and VI) are recommended with the goal of improving these patients' quality of life with and without new brain treatments, beyond the benefits of available peripheral enzyme replacement therapy. Recommendations are offered at-a-glance with respect to what areas most urgently need attention to clarify neurocognitive function in all MPS types.

Novel therapies for mucopolysaccharidosis type III

Mucopolysaccharidosis type III (MPS III) or Sanfilippo disease is an orphan inherited lysosomal storage disease and one of the most common MPS subtypes. The classical presentation is an infantile-onset neurodegenerative disease characterised by intellectual regression, behavioural and sleep disturbances, loss of ambulation, and early death. Unlike other MPS, no disease-modifying therapy has yet been approved. Here, we review the numerous approaches of curative therapy developed for MPS III from historical ineffective haematopoietic stem cell transplantation and substrate reduction therapy to the promising ongoing clinical trials based on enzyme replacement therapy or adeno-associated or lentiviral vectors mediated gene therapy. Preclinical studies are presented alongside the most recent translational first-in-man trials. In addition, we present experimental research with preclinical mRNA and gene editing strategies. Lessons from animal studies and clinical trials have highlighted the importance of an early therapy before extensive neuronal loss. A disease-modifying therapy for MPS III will undoubtedly mandate development of new strategies for early diagnosis.

Is the eye a window to the brain in Sanfilippo syndrome?

Sanfilippo syndrome is an untreatable form of childhood-onset dementia. Whilst several therapeutic strategies are being evaluated in human clinical trials including i.v. delivery of AAV9-based gene therapy, an urgent unmet need is the availability of non-invasive, quantitative measures of neurodegeneration. We hypothesise that as part of the central nervous system, the retina may provide a window through which to 'visualise' degenerative lesions in brain and amelioration of them following treatment. This is reliant on the age of onset and the rate of disease progression being equivalent in retina and brain. For the first time we have assessed in parallel, the nature, age of onset and rate of retinal and brain degeneration in a mouse model of Sanfilippo syndrome. Significant accumulation of heparan sulphate and expansion of the endo/lysosomal system was observed in both retina and brain pre-symptomatically (by 3 weeks of age). Robust and early activation of micro- and macroglia was also observed in both tissues. There was substantial thinning of retina and loss of rod and cone photoreceptors by ~ 12 weeks of age, a time at which cognitive symptoms are noted. Intravenous delivery of a clinically relevant AAV9-human sulphamidase vector to neonatal mice prevented disease lesion appearance in retina and most areas of brain when assessed 6 weeks later. Collectively, the findings highlight the previously unrecognised early and significant involvement of retina in the Sanfilippo disease process, lesions that are preventable by neonatal treatment with AAV9-sulphamidase. Critically, our data demonstrate for the first time that the advancement of retinal disease parallels that occurring in brain in Sanfilippo syndrome, thus retina may provide an easily accessible neural tissue via which brain disease development and its amelioration with treatment can be monitored.

A systematic review and meta-analysis of published cases reveals the natural disease history in multiple sulfatase deficiency

Multiple Sulfatase Deficiency (MSD, MIM#272200) is an ultra-rare lysosomal storage disorder arising from mutations in the SUMF1 gene, which encodes the formylglycine-generating enzyme (FGE). FGE is necessary for the activation of sulfatases, a family of enzymes that are involved in the degradation of sulfated substrates such as glycosaminoglycans and sulfolipids. SUMF1 mutations lead to functionally impaired FGE and individuals with MSD demonstrate clinical signs of single sulfatase deficiencies, including metachromatic leukodystrophy (MLD) and several mucopolysaccharidosis (MPS) subtypes. Comprehensive information related to the natural history of MSD is missing. We completed a systematic literature review and a meta-analysis on data from published cases reporting on MSD. As available from these reports, we extracted clinical, genetic, biochemical, and brain imaging information. We identified 75 publications with data on 143 MSD patients with a total of 53 unique SUMF1 mutations. The mean survival was 13 years (95% CI 9.8-16.2 years). Seventy-five clinical signs and 11 key clusters of signs were identified. The most frequently affected organs systems were the nervous, skeletal, and integumentary systems. The most frequent MRI features were abnormal myelination and cerebral atrophy. Individuals with later onset MSD signs and survived longer than those with signs at birth. Less severe mutations, low disease burden and achievement of independent walking positively correlated with longer survival. Despite the limitations of our approach, we were able to define clinical characteristics and disease outcomes in MSD. This work will provide the foundation of natural disease history data needed for future clinical trial design.

A basic understanding of mucopolysaccharidosis: Incidence, clinical features, diagnosis, and management

Mucopolysaccharidoses (MPS) are a group of rare lysosomal storage diseases (LSD) with multi-organic and severe symptoms. MPS occur worldwide in various forms though have relative a low incidence. The prevalent type of MPS varies among different continents, indicating that it may be associated with region and ethnic background. Undegraded glycosaminoglycans (GAGs) induced by deficiency of enzymes are the primary cause of MPS. Clinical features differ depending on the specific enzyme deficiency including coarse facial features, cognitive retardation, hepatosplenomegaly, hernias, kyphoscoliosis, corneal clouding, etc. Symptoms of different types are usually similar especially MPS I and II, but may have distinguishable features such as severe neurological problems in MPS III and hydrops fetails in MPS VII. These clinical features contribute to diagnosis, but early and precisely diagnosis in the asymptomatic stage is imperative for better outcomes. Novel approaches including urinary and blood GAG test, enzyme assay and gene test help to diagnose MPS and to determine its subtype. Hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT) are conventional treatment for MPS, but are not effective at treating all MPS. Newer threatments, such as advanced ERT, gene therapy and substrate reduction therapy (SRT), improve therpeutic efficacy. In this review, we update information on the clinical manifestations, diagnosis, and treatment of the different forms of this disease in the hopes of stimulating further interest in MPS.

Molecular Bases of Neurodegeneration and Cognitive Decline, the Major Burden of Sanfilippo Disease

The mucopolysaccharidoses (MPS) are a group of diseases caused by the lysosomal accumulation of glycosaminoglycans, due to genetic deficiencies of enzymes involved in their degradation. MPS III or Sanfilippo disease, in particular, is characterized by early-onset severe, progressive neurodegeneration but mild somatic involvement, with patients losing milestones and previously acquired skills as the disease progresses. Despite being the focus of extensive research over the past years, the links between accumulation of the primary molecule, the glycosaminoglycan heparan sulfate, and the neurodegeneration seen in patients have yet to be fully elucidated. This review summarizes the current knowledge on the molecular bases of neurological decline in Sanfilippo disease. It emerges that this deterioration results from the dysregulation of multiple cellular pathways, leading to neuroinflammation, oxidative stress, impaired autophagy and defects in cellular signaling. However, many important questions about the neuropathological mechanisms of the disease remain unanswered, highlighting the need for further research in this area.